76 MR. E. R. ALSTON ON THE ORDER GLIRES. [Jail. 18, 



with the tibia below or free, not articulating with the calcaneum. 

 Testes abdominal, descending periodically ; vesicular glands present*. 



Section I. Sciuromorpha. 



Premolars present ; when there is more than one in the upper 

 jaw the first is smaller than the others ; grinding-teeth rooted or 

 rootless. Postorbital frontal processes present or absent, infraorbital 

 opening various. Zygomatic arch mainly composed of the malar, 

 which is not supported below by a continuation of the maxillary 

 zygomatic process. Outer walls of pterygoid fossae obsolete ; no inter- 

 pterygoid fissure. Incisive foramina small or moderate, not extending 

 into the maxillaries. Mandible with the angular portion springing 

 from the lower edge of the bony covering of the lower incisor, its 

 outline more or less rounded, not pointed ; coronoid process high and 

 falcate. Clavicles perfect. Fibula persistent as a distinct bone 

 through life, and usually perfectly free. Upper lip usually cleft, 

 muffle small and naked ; nostrils comma-shaped, rounded above. 

 Tail cylindrical and hairy (except in Castoridce). Five families : — 



Family I. Anomalurid^. 



One premolar above and below ; grinding-teeth subequal, not 

 tuberculate, with flat crowns and transverse enamel loops. Skull 

 with postorbital processes obsolete ; infraorbital opening large, sub- 

 ovate ; palate contracted in front, deeply emarginate behind. Six- 

 teen pairs of ribs. Limbs connected by a flying expansion of the skin, 

 supported by a chondrified fascia articulating with the olecranon. 

 Tail long, hairy, with a series of large scales on the lower basal 

 portion. Distribution Ethiopian. Recent genus: — 



Anomalurus, Waterhouse, P. Z. S. 1842, p. 124 . . . (1842). 

 (Characters those of the family.) 



Family II. Sciurid^. 



Two premolars above, and one below; the first upper premolar very 

 small, sometimes deciduous ; grinding-teeth rooted, tubercular (at 

 least in youth). Skull with distinct postorbital processes ; infra- 

 orbital opening small, us>ially placed in front of the maxillary 

 zygomatic process ; palate broad, flat. Twelve or thirteen pairs of 

 ribs. Tail cylindrical, hairy. Two subfamilies : — 



A. SciuriNjE. Incisors compressed. Limbs either free or united 

 {Pteromys) by an expansion, whose fascia articulates with the carpus. 

 Form slender, tail long. Cosmopolitan (exc. Australasian region). 

 Recent genera : — 



1. Pteromys, G. Cuvier, Legons d'Anatomie (1800). 



Limbs united by a flying expansion, the supporting fascia of which 

 articulates with the carpus ; tail long, bushy. Grinders usually 

 soon ground flat, in some tuberculate through life. 

 * Cf. Owen, Coinp. Aiiat. Vert. iii. p. 649. 



